For example, such sensors are used as lambda sensors for determining the oxygen concentration in the exhaust gas of an internal combustion engine. The sensor is provided with an integrated electrical heater in order to bring the gas-sensitive sensor element up to its operating temperature as quickly as possible, i.e., during the warm-up phase of the engine. The sensor element is made of ceramic materials. However, such ceramics are very sensitive to wide temperature fluctuations which result in cracks in the ceramic and bring about malfunctions and even total failure of the sensor. Extreme temperature fluctuations, also referred to as thermal shocks, occur on the surface of the sensor element, e.g., at start or during the warm-up phase of the internal combustion engine, when cold drops of water impact the already heated sensor element. Such drops of water may be formed when, during the warm-up phase, water vapor generated by the engine combustion condenses on cold surfaces of the exhaust system and the sensor, and when drops of water separate from the condensate film which are then entrained by the gas flow thereby reaching the sensor element.
For protecting the sensor element from the impact of droplets of water entrained by the exhaust gas flow, a double protecting tube is provided in a known sensor, used as an exhaust gas sensor (German patent document DE 199 24 319 C2), the double protecting tube, made up of an inner tube and an outer tube which each have gas inlet and outlet apertures, enclosing the section of the sensor element which is exposed to the exhaust gas. At least one inlet aperture of the inner tube and/or at least one inlet aperture of the outer tube, a flow element is situated which redirects the exhaust gas flow, which enters the space enclosed by the inner and outer tubes and/or the interior of the inner tube, toward the particular inner lateral surface of the inner and/or outer tube. The water is thus held on the inner lateral surfaces of the tubes and vaporizes slowly due to the exhaust gas temperature which rises during the increasing warm-up of the engine.